Cable with overcoated non-coplanar groups of fusion spliced optical fibers, and fabrication method

ABSTRACT

A fiber optic cable includes a plurality of fusion spliced optical fibers, with a polymeric overcoating extending over a fusion splice region as well as over a stripped section of each optical fiber proximate to the fusion splice region, wherein the plurality of fusion spliced optical fibers has a non-coplanar arrangement at the fusion splice region. A method for fabricating a fiber optic cable includes fusion splicing first and second pluralities of optical fibers arranged in a respective one-dimensional array to form a plurality of fusion spliced optical fibers, and contacting the fusion splices as well as stripped sections of the fusion spliced optical fibers with polymeric material in a flowable state. Either before or after the contacting step, the method further includes altering a position of at least some of the spliced optical fibers to yield a configuration in which the plurality of fusion spliced optical fibers have a non-coplanar arrangement at the fusion splice region. The method further includes solidifying the polymeric material.

PRIORITY APPLICATION

This application claims the benefit of priority of U.S. ProvisionalApplication No. 62/728,326, filed on Sep. 7, 2018, the content of whichis relied upon and incorporated herein by reference in its entirety.

BACKGROUND

The disclosure relates generally to fiber optic cables incorporatingmultiple groups of protected fusion splices, in addition to methods forfabricating such cables.

Optical fibers are useful in a wide variety of applications, includingthe telecommunications industry for voice, video, and data transmission.In a telecommunications system that uses optical fibers, there aretypically many locations where fiber optic cables, which carry theoptical fibers, connect to equipment or other fiber optic cables. Fiberoptic cables are frequently produced by extruding thermoplastic material(e.g., polyvinylchloride (PVC)) over at least one coated optical fiber.

FIG. 1 is a cross-sectional view of an exemplary coated optical fiber 10that includes a glass core 12, glass cladding 14 surrounding the glasscore 12, and a multi-layer polymer coating 20 (including an innerprimary coating layer 16 and an outer secondary coating layer 18)surrounding the glass cladding 14. The inner primary coating layer 16may be configured to act as a shock absorber to minimize attenuationcaused by any micro-bending of the coated optical fiber 10. The outersecondary coating layer 18 may be configured to protect the innerprimary coating layer 16 against mechanical damage, and to act as abarrier to lateral forces. The outer diameter of the coated opticalfiber 10 may be about 200 μm, about 250 μm, or any other suitable value.Optionally, an ink layer (e.g., having a thickness of about 5 μm) may bearranged over the outer secondary coating layer 18 of the coated opticalfiber 10 to color the fiber (e.g., as is commonly used in ribbonizedfibers), or a coloring agent may be mixed with the coating material thatforms the outer secondary coating layer 18. An additional buffer coating(“buffer”; not shown), may be applied to the coated optical fiber 10 toprovide additional protection and allow for easier handling, effectivelyforming a cable. The buffer may be embodied in a layer of differentmaterial applied to the coating 20, thereby forming a “tight buffer”closely surrounding (intimately contacting and conforming to) thecoating 20. Alternatively, the buffer may be embodied in a pre-formedtube (also known as a furcation tube or buffer tube) that has an innerdiameter larger than the coating 20 and into which the coated opticalfiber 10 is inserted, thereby forming a “loose buffer.” This additionalbuffer typically has an outer diameter of about 900 μm.

In this disclosure, the term “optical fiber” (or “fiber”) will be usedin a generic sense and may encompass bare optical fibers, coated opticalfibers, or buffered optical fibers, as well as optical fibers includingdifferent sections corresponding to these fiber types, unless it isclear from the context which of the types is intended. “Bare opticalfibers” (including “bare glass optical fibers”) or “bare sections” arethose with no coating present on the fiber cladding. “Coated opticalfibers” or “coated sections” include a single or multi-layer coating(typically an acrylic material) surrounding the fiber cladding and havea nominal (i.e., stated) diameter no greater than twice the nominaldiameter of the bare optical fiber. “Buffered optical fibers” or“buffered sections” are coated optical fibers with an additional bufferthat increases the nominal diameter of the optical fiber to more thantwice the nominal diameter of the bare optical fiber, with 900 μm beingthe most typical nominal diameter. Buffered optical fibers may also bereferred to as “buffered cables.” Finally, the term “unbuffered opticalfibers” refers to optical fibers without a buffer, and therefore mayencompass either bare optical fibers or coated optical fibers.

Optical fiber fusion splicing, which is the process by which apermanent, low-loss, high-strength, fused (or welded) joint is formedbetween two optical fibers, typically involves multiple tasks. First,polymer coatings (e.g., coating layers 16, 18 of FIG. 1) of coatedoptical fibers (e.g., coated optical fiber 10 of FIG. 1) are stripped toexpose glass cladding (e.g., glass cladding 14 of FIG. 1). Next, flatfiber end faces are formed, typically by cleaving exposed glass portionsof the fibers. Then the fibers are laterally aligned to each other. Thefiber tips must be heated to their softening point and pressed togetherto form a joint. Checks such as loss estimation and proof testing (toensure long term mechanical reliability) may be performed. The completedfusion splice must also protected from the environment using packaging,which serves to shield fiber surfaces from mechanical degradation (e.g.,abrasion) and chemical degradation (e.g., humidity) to ensure thatsplices exhibit long-term reliability. Optical fibers must typically beable to withstand service temperatures spanning at least a range of from−40° C. to 85° C. without suffering significant mechanical and/oroptical performance degradation.

Heat shrink protection sleeves are commonly used as packaging to protectspliced optical fibers. Such a sleeve typically includes an outer heatshrink tube (typically made of a heat shrinkable material (e.g., apolyolefin) and/or a non-stick material (e.g., polytetrafluoroethylene(PTFE)), an inner thermoplastic tube typically made of a melt flowadhesive material (e.g., ethylene vinyl acetate (EVA)), and a stainlesssteel rod serving as the strength member or splint. When heated in anoven (e.g., associated with a fusion splicing tool), the thermoplastictube melts and is compressed around the fiber and the stainless steelrod by the heat shrink tube, forming a hermetic seal around the fusionsplice region.

FIG. 2 illustrates a first exemplary heat shrink protection sleeve 28that includes an outer heat shrink tube 26, an integrated (e.g.,stainless) steel strength member 24 (e.g., a stainless steel rod orsplint) integrated with and contained in the outer heat shrink tube 26,and an inner thermoplastic tube 22 within which the coated optical fiber10 of FIG. 1 is arranged. The inner primary coating layer 16 and outersecondary coating layer 18 of the multi-layer polymer coating 20 are notillustrated in FIG. 2 to simplify the drawing. The outer heat shrinktube 26 and the inner thermoplastic tube 22 are shown in FIG. 2 in an“unshrunken” state (prior to application of heat thereto), with theinner thermoplastic tube 22 being loosely fitted around the opticalfiber 10, and with the outer heat shrink tube 26 being loosely fittedaround the integrated strength member 24 and the inner thermoplastictube 22. It is to be appreciated that following application ofsufficient heat, the inner thermoplastic tube 22 will soften and/or meltto more closely conform to the exterior of the optical fiber 10, and theouter heat shrink tube 26 will contract around the stainless steelstrength member 24 and the inner thermoplastic tube 22. The purpose ofthe integrated strength member 24 is to resist bending and enhancetensile strength, thereby enhancing reliability of a splice—particularlywhen an optical fiber containing the splice needs to be coiled in atight space.

Another exemplary heat shrink protection sleeve 30 used to protect asplice joint 32 formed between two coated optical fibers 10A, 10B isschematically illustrated in FIGS. 3A and 3B. The heat shrink protectionsleeve 30 includes a generally cylindrical inner tube 34 (e.g., a meltflow adhesive material such as ethylene vinyl acetate (EVA)) and agenerally cylindrical outer tube 36 (e.g., a polyolefin and/or PTFE),wherein the outer tube 36 generally surrounds the inner tube 34, and theinner tube 34 defines an interior passage 40. The outer tube 36 isrequired for conventional heat shrink protection sleeves because themelt flow adhesive material (e.g., EVA) has a very high viscosity and avery low softening temperature (e.g., about 100° C.). The moretemperature-resistant outer tube 36 is typically consideredindispensable, particularly when the splice is intended for operationover a high temperature range of up to about 85° C. In use, the heatshrink protection sleeve 30 is positioned over a fusion spliced sectionof two optical fibers 10A, 10B. The fusion spliced section includes asplice joint 32 arranged between (stripped) glass cladding segments 14A,14B of the respective optical fibers 10A, 10B. Upon application of heat(typically within an oven), the inner tube 34 melts around the opticalfibers 10A, 10B, the glass cladding segments 14A, 14B, and the splicejoint 32. The outer tube 36, which includes a cylindrical outer surface38, may include some heat shrinking capability to help the adhesivedistribute around the fused optical fibers 10A, 10B.

As the de facto splice protection technology in the fiber opticsindustry for decades, limitations of heat shrink protection sleeves arewell known. Firstly, an operator must remember to thread (i.e., guide)an optical fiber through the heat shrink protection sleeve before fusionsplicing is performed. A misstep in this process may require breakingand reworking the splice. Secondly, an optical fiber is subject to beingthreaded in the wrong place when the splice protector is small indiameter. If the optical fiber is in a cavity inside the outer tube butoutside the inner tube (e.g., such as the inner and outer tubes 22, 26of FIG. 2), the optical fiber will be in direct contact with thestainless steel strength member, which can weaken or break the fiber.Thirdly, curing the heat shrink protection sleeve can take at least 30seconds, with such duration representing the longest and rate-limitingfraction of the time necessary to complete a single fusion splicingcycle. Additionally, fusion splices protected with heat shrinkprotection sleeves are bulky and inflexible, necessitating the use of asplice tray, module, or the like to manage the protection sleeves. Thisincreases the cost and limits the size (i.e., miniaturization) of fiberoptic components that contain fusion splices. Lastly, in cable assemblyapplications, a heat shrink protection sleeve requires excess jacketstrip length, which requires an extra process step and extra material toprotect the exposed cable after splicing.

Groups of coated optical fibers (e.g. 4, 8, 12, or 24 optical fibers)may be held together using a matrix material, intermittent inter-fiberbinders (“spiderwebs”), or tape to form “optical fiber ribbons” or“ribbonized optical fibers” to facilitate packaging within cables. Forexample, optical fiber ribbons are widely used in cables for highcapacity transmission systems. Some modern cables in large-scale datacenters or fiber-to-the-home networks may contain up to 3,456 opticalfibers, and cables having even higher optical fiber counts are underdevelopment. Optical fibers that form a ribbon are arranged in parallelin a linear (i.e., one-dimensional) array, with each fiber having adifferent color for ease of identification. FIG. 4 provides across-sectional view of a multi-fiber ribbon 42, which includes twelveoptical fibers 44A-44L and a matrix 46 encapsulating the optical fibers44A-44L. The optical fibers 44A-44L are substantially aligned with oneanother in a generally parallel configuration, preferably with anangular deviation of no more than one degree from true parallel at anyposition. Although twelve optical fibers 44A-44L are shown in the ribbon42, it is to be appreciated that any suitable number of multiple fibers(but preferably at least four fibers) may be employed to form opticalfiber ribbons suitable for a particular use.

Mass fusion splicing is a high throughput technology for interconnectinglarge number of fibers in a ribbon format. First and second segments ofup to twelve fibers arranged in a linear array can be fusion splicedsimultaneously by mass fusion splicing. Since sequential formation oftwelve fusion splices using a traditional single fiber fusion splicingtechnique is very time consuming, the ability to fusion splice linearlyarrayed segments of up to twelve fibers simultaneously enables entireribbons to be spliced rapidly, thereby improving manufacturingthroughput. Mass fusion splicing also allows for potential materialsavings. It enables migration from common indoor distribution cableswith 900 μm fibers to smaller mini-distribution cables with 250 μm or200 μm fibers, which is more cost-effective.

Heat shrink protection sleeves similar to those outlined above have alsobeen applied to protect optical fiber ribbon splices, which includemultiple fusion splices between first and second arrays of paralleloptical fibers contained in first and second optical fiber ribbonsegments, respectively. In such a context, an integrated strength membertypically includes a flat surface to support the fusion spliced fiberarrays, a thermoplastic inner tube is melted around the spliced ribboncables and the integrated strength member, and a moretemperature-resistant outer tube encases the thermoplastic inner tube.The cross section of a typical ribbon splice protector is 4 mm×4.5 mm,and the length is about 40 mm. Such a splice protector is suitable forinterfacing with optical fiber ribbons, but not jacketed cables sincethe cross-sectional width of a ribbon-type splice protector is muchlarger than that of a jacketed cable.

For end uses requiring smaller cable widths, loose tube cables having around cross section with an outer diameter of 2 mm or 3 mm are commonlyemployed. Alternatively, a round cable may include a rollable opticalfiber ribbon, such as disclosed in U.S. Patent Application PublicationNo. 2017/0031121 A1 (with the content of such publication beingincorporated by reference herein). As noted in such publication, arollable optical fiber ribbon includes a ribbon body formed overflexible polymeric material such that a plurality of optical fibers arereversibly movable between a position in which the optical fibers arearranged in a one-dimensional array and a position in which the opticalfibers are arranged in a curved shape from a cross-sectional view.

Unfortunately, current mass fusion splice technology, as well as currentfusion splice protection technology, only support one-dimensional arraysof optical fiber splices. For splicing of fibers of small diameter roundcables, it is necessary to ribbonize loose tube fibers or arrangerollable optical fiber ribbons in a one-dimensional array to permit massfusion splicing, and the mass fusion spliced one-dimensional array offibers is typically protected in a bulky heat shrink sleeve. FIG. 5illustrates a conventional cable assembly 50 incorporating first andsecond loose tube-type cables 52A, 52B bearing pre-coated loose opticalfibers 54A, 54B, with stripped sections thereof that are mass fusionspliced in a one-dimensional array in a fusion splice region 56 that isprotected by a conventional ribbon splice protector 60. The ribbonsplice protector 60 includes an outer heat shrink member 64 and an innerthermoplastic member 62 that surrounds the fusion splice region 56 aswell as stripped sections (not shown) of the loose optical fibers 54A,54B. As shown in FIG. 5, the ribbon splice protector 60 has a muchlarger diameter or width than a diameter or width of each of the loosetube-type cables 52A, 52B. Moreover, the width of each one-dimensionalarray of optical fibers 54A, 54B proximate to the inner thermoplasticmember 62 is also greater than the diameter of each of the first andsecond loose tube-type cables 52A, 52B. The benefits of small roundcables are thus completely defeated if a cable assembly incorporatingsmall round cables involves a fusion splice connection. The size ofconventional one-dimensional array splice protection technology islimiting the practical attainment of higher fiber density in fiber opticmodules and cable assemblies.

Another conventional method for protecting fusion splices is splicerecoating. In a recoating process, a stripped and spliced fiber sectionis placed in a mold with an inner diameter matching the fiber coatingdiameter. Typically, UV-sensitive polymer recoat material (e.g.,acrylate-based material) is injected into the mold to surround the bareglass cladding of the spliced fibers, and UV light cures the polymerrecoat material in place to yield a recoated optical fiber having thesame cross-sectional dimension as that of the original coated fiber.Fiber recoaters are manufactured by companies such as America FujikuraLtd. (AFL) and Vytran (a division of Thorlabs, Inc.). While recoatingprovides benefits such as reduced size and increased flexibilityrelative to the use of heat shrink protection sleeves, the use ofrecoating has been limited to high-end applications such as submarinefiber fusion splicing. While recoated splices offer higher density thanribbon-type splice protectors, the absence of a strength member rendersa splice region subject to bending, which may pose a long-termreliability concern. Moreover, even though recoating may attain a spliceprotector offering the same size as a flat ribbon, a resulting coatedarray of twelve one-dimensional fiber splices remains too wide to fitinto a standard 2 mm or 3 mm outer diameter round cable jacket.

In view of the foregoing need remains in the art for high densitymulti-fiber cables and cable assemblies incorporating fusion splicesthat address the above-described and other limitations associated withconventional one-dimensional array-type splice protectors, as well asassociated fabrication methods.

SUMMARY

Aspects of the present disclosure provide a fiber optic cable includinga plurality of fusion spliced optical fibers, with a polymericovercoating extending over a fusion splice region as well as over astripped section of each optical fiber proximate to the fusion spliceregion, and with the plurality of fusion spliced optical fibers having anon-coplanar arrangement at the fusion splice region. A method forfabricating a fiber optic cable is also provided. Such a methodcomprises mass fusion splicing ends of first and second pluralities ofoptical fiber segments when arranged in aligned one-dimensional arraysto form a plurality of fusion spliced optical fibers and define a fusionsplice region. A further step comprises contacting the fusion splices aswell as stripped sections of the spliced optical fibers with polymericmaterial in a flowable state. Either before or after the contactingstep, the method further comprises altering a position of at least someof the fusion spliced optical fibers to yield a configuration in whichthe plurality of fusion spliced optical fibers have a non-coplanararrangement at the fusion splice region. The method additionallycomprises solidifying the polymeric material.

To be clear, “fusion splice region” refers to a location or length ofthe fiber optic cable that includes the fusion splices between theoptical fiber segments. If all the fusion splices are aligned in aplane, the fusion splice region is the location of that plane along thelength of the fiber optic cable. If the fusion splices are notco-planer, the fusion splice region is defined between the two fusionsplices that are furthest apart along the length of the fiber opticcable. Thus, term “fusion splice region” is not intended to includelonger lengths of the fiber optic cable extending from the fusionsplices.

In one embodiment of the disclosure, a fiber optic cable is provided.The fiber optic cable comprises a plurality of fusion spliced opticalfibers. Each fusion spliced optical fiber includes two optical fibersegments joined together by a fusion splice, and each optical fibersegment includes a stripped section proximate to the fusion splice. Thefiber optic cable further comprises a polymeric overcoating extendingover the fusion splices and over the stripped section of each opticalfiber segment. The fusion splices of the plurality of fusion splicedoptical fibers define a fusion splice region of the fiber optic cable,and the plurality of fusion spliced optical fibers has a non-coplanararrangement at the fusion splice region.

In accordance with another embodiment of the disclosure, a method forfabricating a fiber optic cable is provided. The method comprisesarranging ends of a first plurality of optical fiber segments and endsof a second plurality of optical fiber segments in respectiveone-dimensional arrays that are aligned with one other. The methodadditionally comprises mass fusion splicing the ends of the firstplurality of optical fiber segments to the ends of the second pluralityof optical fiber segments to form a plurality of fusion spliced opticalfibers each incorporating one optical fiber segment of the firstplurality of optical fiber segments and one optical fiber segment of thesecond plurality of optical fiber segments. Fusion splices between theends of the first plurality of optical fiber segments and the ends ofthe second plurality of optical fiber segments define a fusion spliceregion of the fiber optic cable, and each optical fiber segment of thefirst and second pluralities of optical fiber segments includes astripped section proximate the fusion splice region. The method furthercomprises contacting the fusion splices of the plurality of fusionspliced optical fibers as well as at least a portion of the strippedsection of each optical fiber segment with a polymeric material in aflowable state, The method additionally comprises altering position ofat least some fusion spliced optical fibers of the plurality of fusionspliced optical fibers to yield a configuration in which the pluralityof fusion spliced optical fibers has a non-coplanar arrangement at thefusion splice region. The method further comprises solidifying thepolymeric material with the plurality of fusion spliced optical fibersin the non-coplanar arrangement at the fusion splice region.

In one embodiment of the disclosure, a fiber optic cable is provided.The fiber optic cable comprises first and second groups of fusionspliced optical fibers, wherein each fusion spliced optical fiberincludes two optical fiber segments joined together by a fusion splice,each optical fiber segment includes a stripped section proximate to thefusion splice of the corresponding fusion spliced optical fiber. Apolymeric overcoating extends over the fusion splices and over thestripped section of each optical fiber segment. The fusion splicesdefine a fusion splice region of the fiber optic cable. The first groupand the second group of fusion spliced optical fibers are arranged inrespective first and second planes at the fusion splice region. Thefirst and second planes extend in a lengthwise direction of the fiberoptic cable and are definable through fiber cores of the respectivefirst group and second group of fusion spliced optical fibers, and thefirst and second planes are non-coplanar.

Additional features and advantages will be set forth in the detaileddescription that follows, and in part will be readily apparent to thoseskilled in the technical field of optical connectivity. It is to beunderstood that the foregoing general description, the followingdetailed description, and the accompanying drawings are merely exemplaryand intended to provide an overview or framework to understand thenature and character of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding, and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiment(s), andtogether with the description serve to explain principles and operationof the various embodiments. Features and attributes associated with anyof the embodiments shown or described may be applied to otherembodiments shown, described, or appreciated based on this disclosure.

FIG. 1 is a cross-sectional view of a conventional coated optical fiberthat may be subject to fusion splicing, prior to stripping of amulti-layer polymer coating from glass cladding.

FIG. 2 is a cross-sectional view of a conventional splice protectorincluding a heat shrink protection sleeve and an integrated strengthmember.

FIG. 3A is a schematic perspective view of a conventional heat shrinkprotection sleeve used to protect a splice joint between two opticalfibers.

FIG. 3B is a schematic cross-sectional view of the heat shrinkprotection sleeve and optical fibers of FIG. 3A, with schematicillustration of the splice joint between stripped portions of the twooptical fibers.

FIG. 4 is a cross-sectional view of a conventional optical fiber ribbonincluding twelve optical fibers.

FIG. 5 illustrates segments of two small round-type fiber optic cablesfrom which twelve loose fibers extend, with the loose fibers beingspliced in a one-dimensional array and protected by a conventionalmulti-fiber heat shrink protection sleeve.

FIG. 6 is a schematic side view illustration of a fusion spliced sectionof optical fibers including a solid overcoating of thermoplasticmaterial having a substantially constant thickness but an outer diameterthat varies along intermediate portions thereof, with the solidovercoating of thermoplastic material arranged over stripped sections ofthe first and second optical fibers, a splice joint, and pre-coatedsections of the first and second optical fibers.

FIG. 7A is an upper perspective view illustration of a bare, mass fusionspliced section of two multi-fiber ribbon segments forming a splicedribbon cable, with a first lateral edge portion of the spliced ribboncable submerged in a pool of molten thermoplastic material atop asubstantially level, flat heated surface, and with the ribbon cablebeing tilted at an approximately forty-five degree angle during a ribboncable insertion step, such that a second lateral edge portion of thespliced ribbon cable is arranged at a level above the first lateral edgeportion.

FIG. 7B illustrates the items of FIG. 7A, with the entire mass fusionspliced section of the spliced ribbon cable disposed in the pool ofmolten thermoplastic material atop the substantially level, flat heatedsurface, and with the first lateral edge portion being arranged atsubstantially the same horizontal level as the second lateral edgeportion of the spliced ribbon cable.

FIG. 8A is a perspective view of a portion of a fiber optic cable withnon-coplanar groups of fusion spliced optical fibers that form a 3×4array, and overcoating material that extends over stripped sections ofthe fusion spliced optical fibers and the splice region.

FIG. 8B is a cross-sectional view of the fiber optic cable of FIG. 8A.

FIG. 9A is a perspective view of a portion of a fiber optic cable withnon-coplanar groups of fusion spliced optical fibers that form a 2×6array, and overcoating material that extends over stripped sections ofthe fusion spliced optical fibers and the splice region.

FIG. 9B is a cross-sectional view of the fiber optic cable of FIG. 9A.

FIG. 10A is a perspective view of a portion of a fiber optic cable withnon-coplanar groups of fusion spliced optical fibers that form ahexagonal close packed four-layer configuration, and overcoatingmaterial that extends over stripped sections of the fusion splicedoptical fibers and the splice region.

FIG. 10B is a cross-sectional view of the fiber optic cable of FIG. 10A.

FIG. 11A is a perspective view of a portion of a fiber optic cablesubassembly during fabrication, showing a one-dimensional array oftwelve fusion spliced optical fibers, following adhesive binding ofpre-coated sections of the fusion spliced optical fibers to maintainpositioning of optical fibers in preparation for thermoplasticovercoating.

FIG. 11B is a perspective view of a completed portion of a fiber opticcable incorporating the subassembly of FIG. 11A, following addition ofpolymeric overcoating material that extends over stripped sections ofthe fusion spliced optical fibers, the splice region, and portions ofthe adhesively bound pre-coated sections.

FIG. 12A is a perspective view of a portion of a fiber optic cablesubassembly during fabrication, showing a two-dimensional array ofmultiple fusion spliced optical fibers in a process of being formed byrolling in a direction perpendicular to cores of the fusion splicedoptical fibers.

FIG. 12B is a perspective view of a portion of a fiber optic cablesubassembly during fabrication, showing an overcoated first group offusion spliced optical fibers in a state of being folded to overlap anovercoated second group of fusion spliced optical fibers.

FIG. 13 is a perspective view of a portion of an overcoated fiber opticcable assembly arranged on a heated surface during fabrication, to causereflow of polymeric overcoating material that extends over strippedsections of the fusion spliced optical fibers and the splice region.

FIG. 14A provides a comparison between (top) a conventional ribbonspliced cable assembly including optical fiber ribbons spliced in aone-dimensional array format, and (bottom) a fiber optic cable assemblyaccording to one embodiment including groups of twelve loose opticalfibers fusion bonded to one another and positioned in a hexagonal closepacked four-layer configuration, with a thermoplastic overcoatingmaterial protecting the splice region.

FIG. 14B illustrates the second (bottom) fiber optic cable assembly ofFIG. 14A bent into a tight radius to demonstrate that the overcoatedsplice region exhibits greater stiffness than non-overcoated strandedfibers.

DETAILED DESCRIPTION

Various embodiments will be further clarified by examples in thedescription below. In general, the description relates to a fiber opticcable with overcoated non-coplanar groups of fusion spliced opticalfibers, and a method for fabricating such a cable. The cable may be partof a cable assembly in which at least some of the fusion spliced opticalfibers are terminated with fiber optic connectors.

In this disclosure, the language “fusion spliced optical fiber” refersto two optical fibers that have been fusion spliced together to form apermanent, optical link incorporating the two optical fibers. Thesingular noun “fusion spliced optical fiber” is used even though twooptical fibers are initially present because, after fusion splicing, theresulting optical link is intended to function like a continuous opticalfiber (even though there may be some attenuation resulting from thefusion splice joint). Using the singular form also facilitatesdiscussions involving groups of these fusion spliced optical fibers, aswill be apparent.

Likewise, in this disclosure, the two optical fibers that define a given“fusion spliced optical fiber” may alternatively be referred to as“optical fiber segments.” Using the language “optical fiber segments”rather than “optical fibers” helps clarify when the disclosure isreferring to one of the pairs of optical fibers that form one of thefusion spliced optical fibers, versus one of the fusion spliced opticalfibers itself.

As will be discussed in more detail below, one exemplary aspect relatesto a fiber optic cable that includes a plurality of fusion splicedoptical fibers, with each fusion spliced optical fiber including twooptical fiber segments that are arranged serially and joined together bya fusion splice. The fiber optic cable also includes a polymericovercoating extending over the fusion splices of the plurality of fusionspliced optical fibers as well as over a stripped section of eachoptical fiber segment proximate to the fusion splice of thecorresponding fusion spliced optical fiber (i.e., the fusion splice thatjoins the optical fiber segment in question to the other optical fiberof the serial arrangement). The fusion splice joints of the plurality offusion spliced optical fibers define a fusion splice region of the fiberoptic cable, and the plurality of fusion spliced optical fibers have anon-coplanar arrangement at the fusion splice region.

A “non-coplanar arrangement” in the fusion splice region is anarrangement in which the optical fibers of a plurality of fusion splicedoptical fibers are not exclusively aligned (or exclusive substantiallyaligned) in a common plane that extends in a lengthwise direction of thefiber optic cable. In other words, there is no common plane, extendingin a lengthwise direction of the fiber optic cable, that intersects allfusion spliced optical fibers at the fusion splice region (i.e., nosubstantial alignment in a common plane); or more specifically, there isno common plane, extending in a lengthwise direction of the fiber opticcable, that intersects a fiber core or each of the fusion splicedoptical fibers at the fusion spliced region (i.e., no alignment in acommon plane). Thus, “substantial alignment” refers to the fusionspliced optical fibers in general, whereas “alignment” is more preciseand refers to fiber cores of the fusion spliced optical fibers. As canbe appreciated, due to the non-coplanar arrangement at the fusion spliceregion, the fusion spliced optical fibers are not exclusively arrangedin a one-dimensional array in a cross-sectional view perpendicular tothe lengthwise direction of the fiber optic cable. Such an arrangementdoes not preclude the presence of two or more groups of fusion splicedoptical fibers arranged in different one-dimensional arrays that incombination form a multi-dimensional array, so long as all fusionspliced optical fibers of the plurality of fusion spliced optical fibersare not arranged in a single one-dimensional array. The non-coplanararrangement of fusion spliced optical fibers can be expressed byconsidering there to be multiple groups of the fusion spliced opticalfibers, still with a polymeric overcoating extending over a fusionsplice region as well as over a stripped section of each optical fibersegment. To this end, a first group of the fusion spliced optical fibersis arranged non-coplanar to a second group of the fusion spliced opticalfibers at the fusion splice region.

As noted previously, current mass fusion splice technology and currentfusion splice protection technology only support one-dimensional arraysof optical fiber splices. A fiber optic cable as disclosed herein mayinclude mass fusion spliced optical fibers that are repositioned (afterfusion splicing is completed) to a configuration other than aone-dimensional array, and overcoated or encapsulated with polymericmaterial.

In another exemplary aspect, a method for fabricating a fiber opticcable includes mass fusion splicing first and second pluralities ofoptical fiber segments arranged in a one-dimensional array to form aplurality of fusion spliced optical fibers. A further step includescontacting stripped sections of the fusion spliced optical fibers withpolymeric material in a flowable state. Either before or after thecontacting step, the method further includes altering position of (i.e.,rearranging) at least some of the fusion spliced optical fibers to yielda configuration in which the fusion spliced optical fibers have anon-coplanar arrangement at the fusion splice region. The method furtherincludes solidifying the polymeric material with the fusion splicedoptical fibers in the non-coplanar arrangement at the fusion spliceregion.

In certain embodiments, the solidified polymeric material forms apolymeric overcoating that encapsulates the fusion splice region and thestripped sections of each optical fiber segment of the plurality offusion spliced optical fibers. Such overcoating may also extend over aportion of a pre-coated (unstripped) section of each optical fiber.

The altering of position of at least some of the fusion spliced opticalfibers to yield a configuration in which the plurality of fusion splicedoptical fibers have a non-coplanar arrangement at the fusion spliceregion may be performed either before or after the fusion splicedoptical fibers are contacted with polymeric material in a flowablestate. In certain embodiments, the contacting of the fusion splices aswell as at least a portion of the stripped sections of the fusionspliced optical fibers with a polymeric material in a flowable state isperformed prior to the altering of position of at least some fusionspliced optical fibers. Conversely, in certain embodiments, thecontacting of the fusion splices as well as at least a portion of thestripped sections of the fusion spliced optical fibers with a polymericmaterial in a flowable state is performed after the altering of positionof at least some fusion spliced optical fibers. In certain embodiments,the contacting of at least a portion of the stripped sections withpolymeric material in a flowable state comprises (i) coating at least aportion of the stripped sections with a first portion of polymericmaterial prior to the altering of position of at least some fusionspliced optical fibers; and (ii) coating at least a portion of thestripped sections with a second portion of polymeric material prior tothe altering of position of at least some fusion spliced optical fibers.In certain embodiments, the first portion of polymeric material may becompositionally the same as the second portion of polymeric material, orthe first and second portions of polymeric material may becompositionally different.

Various methods may be used to solidify polymeric material in a flowablestate, depending on the character of the polymeric material. In certainembodiments, polymeric material may be solidified by supplying achemical (e.g., a polymerization agent, which may optionally includewater) to promote cross-linking between polymer chains. In certainembodiments, solidifying of the polymeric material may be accomplishedby cooling the polymeric material. In certain embodiments, thecontacting of at least a portion of the stripped section of each opticalfiber segment of the plurality of fusion spliced optical fibers with thepolymeric material in a flowable state is performed prior to thealtering of position of at least some fusion spliced optical fibers, andthe altering of position of at least some fusion spliced optical fibersis performed while the polymeric material in a flowable state ismaintained at a melt flow temperature of the polymeric material.

In certain embodiments, polymeric material may be in a flowable statewhen initially contacted with stripped sections of optical fibersegments and fusion splices, at least partially solidified, andsubsequently reflowed and resolidified. In certain embodiments, thecontacting of at least a portion of the stripped sections of eachoptical fiber segment of the plurality of fusion spliced optical fiberswith the polymeric material in a flowable state comprises coating thestripped sections with the polymeric material in a flowable state, andthe contacting is performed prior to the altering of position of atleast some fusion spliced optical fibers of the plurality of fusionspliced optical fibers. Thereafter, the altering of position of at leastsome fusion spliced optical fibers of the plurality of fusion splicedoptical fibers comprises stacking a first group of fusion splicedoptical fibers of the plurality of fusion spliced optical fibers over asecond group of fusion spliced optical fibers of the plurality of fusionspliced optical fibers with polymeric material coated on the strippedsections during the contacting step arranged therebetween. In such acase, the polymeric material may be reheated after the altering ofposition of at least some fusion spliced optical fibers of the pluralityof fusion spliced optical fibers to reflow and merge polymeric materialarranged between (i) the first group of fusion spliced optical fibersand (ii) the second group of fusion spliced optical fibers.

In certain embodiments, at the fusion splice region following thealteration of position of at least some fusion spliced optical fibers, afirst plane is definable through fiber cores of at least two fusionspliced optical fibers of a first group of fusion spliced opticalfibers, a second plane is definable through fiber cores of at least twofusion spliced optical fibers of a second group of fusion splicedoptical fibers, and the first and second planes are non-coplanar.Relative to maintaining the fusion spliced optical fibers in a singleone-dimensional array, repositioning of the spliced optical fibersserves to reduce aggregate lateral dimensions of the fusion splicedoptical fibers. The fusion spliced optical fibers and the polymericmaterial effectively form a composite that strongly resists torsion andbending in any direction, with the fusion spliced optical fiberscollectively reinforcing one another. In certain embodiments, a fiberoptic cable with overcoated non-coplanar groups of fusion splicedoptical fibers may be devoid of a strength member spanning over thefusion splice region and/or may be devoid of heat shrink tubing arrangedover the fusion splice region. In other embodiments, fiber optic cablewith overcoated non-coplanar groups of fusion spliced optical fibers mayinclude a strength member (e.g., a metal member, an additional polymerlayer or material, a ceramic material, etc.) spanning over the fusionsplice region. If an added strength member is provided, then suchstrength member may be adhered to an exterior of an polymericovercoating material in certain embodiments.

The preceding reference to non-coplanar first and second planesdefinable through fiber cores of first and second groups of fusionspliced optical fibers, respectively, is neither intended to limit, norserves to limit, the subject matter disclosed herein to fusion splicedoptical fibers in a “two row” array. Any suitable configuration forarranging multiple groups of fusion spliced optical fibers, other thanexclusively in a one-dimensional array, is contemplated by suchlanguage. In certain embodiments, a third group of fusion splicedoptical fibers may be further provided, wherein at the fusion spliceregion, a third plane is definable through substantially parallel fibercores of at least two optical fibers of the third group of fusionspliced optical fibers, with the first, second, and third planes beingnon-coplanar. In certain embodiments involving a total of twelve fusionspliced optical fibers, the fusion splice region may be configured as a2×6 array, a 3×4 array, or a hexagonal close packed four-layerconfiguration, respectively. In certain embodiments, fusion splicedoptical fibers may be placed in a spiral configuration so long as thefusion spliced optical fibers remain substantially parallel to oneanother (e.g., within one degree or within two degrees of deviation fromparallel at any one position). Other configurations may be provided forgroups of twelve fusion spliced fibers or for groups of fusion splicedfibers other than twelve in number. In certain embodiments, each groupof optical fiber segments to be spliced may include 8, 12, 16, or 24optical fibers. Other numbers of optical fibers may be provided. Incertain embodiments, non-coplanar first and second groups of fusionspliced optical fibers each include at least three, or at least four,fusion spliced optical fibers. Such optical fibers may include singlemode optical fibers or multi-mode optical fibers.

In certain embodiments, pre-coated (i.e., acrylate coated) opticalfibers subject to being fusion bonded and overcoated (or encapsulated)according to methods disclosed herein are prepared for fusion bonding(e.g., by stripping ends thereof) utilizing non-contact fiber strippingmethods and/or apparatuses, such as those disclosed in U.S. Pat. No.9,167,626 (“the '626 Patent”), which is hereby incorporated byreference. Briefly, the '626 Patent discloses use of a heater configuredfor heating a heating region to a temperature above a thermaldecomposition temperature of at least one coating of an optical fiber, asecuring mechanism for securely positioning a lengthwise section of theoptical fiber in the heating region, and a controller operativelyassociated with the heater and configured to deactivate the heater nolater than immediately after removal of the at least one coating fromthe optical fiber. Thermal decomposition of at least one coating of anoptical fiber reduces or minimizes formation of flaws in optical fibersthat may be generated by mechanical stripping methods and that canreduce their tensile strength.

It is to be noted that optical fibers of a first plurality of segmentsand of a second plurality of segments to be fusion bonded may bearranged in first and second conventional fiber sorting fixtures,respectively, during the stripping and/or fusion bonding steps. Atypical fiber sorting fixture includes a slot closely each having anopening dimension (e.g., height) that closely matches a correspondingdimension of unbuffered, coated optical fibers to maintain portions ofthe optical fibers proximate to ends to be stripped (and subsequentlyfusion spliced) in fixed, substantially parallel positions embodying aone-dimensional array. In certain embodiments, coated optical fibershaving outer diameters of either 200 μm or 250 μm may laterally abut oneanother in a fiber sorting fixture, such that cores of adjacent opticalfibers are also spaced either 200 μm or 250 μm apart. After stripping ofacrylate coating material from end sections (to form stripped sections)of the optical fibers, the remaining (bare glass) cladding and coreportions are in a non-contacting (and non-crossing) relationship, andbare glass ends of the optical fibers may be fusion bonded usingconventional fusion bonding method steps known to those skilled in theart. Mass fusion bonding may be used in any embodiments disclosedherein. Variations of the techniques disclosed in the '626 Patent aredisclosed in U.S. Patent Application Publication Nos. 2016/0349453 and2017/0001224, the disclosures of which are also hereby incorporated byreference herein. Non-contact stripping methods using lasers or hotgases are also possible in certain embodiments.

After a one-dimensional array of fusion spliced optical fibers is formed(and either before or after at least some optical fibers of theplurality of fusion spliced optical fibers are positioned into aconfiguration other than a one-dimensional array), at least a portion ofthe stripped sections of the fusion spliced optical fibers are contactedwith polymeric material in a flowable state. Such polymeric materialbeneficially overcoats or encapsulates the splice region and strippedsections of the optical fibers, and preferably also overcoats portionsof pre-coated sections of the optical fibers proximate to the strippedsections. In certain embodiments, the maximum width and heightdimensions of the polymeric material in a resulting fiber optic cableare only slightly larger than maximum width and height dimensions of anarray of pre-coated sections of the optical fibers proximate to thestripped sections. For example, in certain embodiments, the largestheight and width portions of the polymeric material may correspond toareas in which the polymeric material overlaps the pre-coated (i.e.,acrylate coated) sections of optical fibers. In certain embodiments, thepolymeric material overlap region has a length of at least 3 mm. If thepolymeric material has a thickness in such regions in a range of from0.05 to 0.3 mm, then in certain embodiments, the greatest height and/orwidth portions of the polymeric material may exceed a greatest heightand/or width portions of a corresponding array of pre-coated sections ofoptical fibers (proximate to the stripped sections of optical fibers) bydimensions in one of the following ranges: a range of from 0.1 to 0.6mm, a range of from 0.2 to 0.6 mm, a range of from 0.1 to 0.5 mm, arange of from 0.2 to 0.5 mm, a range of from 0.2 to 0.4 mm, a range offrom 0.2 to 0.3 mm, a range of from 0.3 to 0.6 mm, or a range of from0.4 mm to 0.6 mm.

To schematically illustrate the result of polymeric overcoating, FIG. 6is a schematic side view illustration of an overcoated fusion splicedoptical fiber 88 composed of optical fiber segments 70A, 70B, in which asolid overcoating 80 of thermoplastic material has a substantiallyconstant outer diameter over the majority of its length. Each opticalfiber segment 70A, 70B includes a coating, with portions of each opticalfiber segment 70A, 70B being previously stripped of such coating to formstripped sections 74A, 74B embodying glass cladding. Ends of thestripped sections 74A, 74B are fusion spliced at a splice joint 72 toform the fusion spliced optical fiber 88. The solid overcoating 80 ofpolymeric material extends over the splice joint 72, the previouslystripped sections 74A, 74B, and short lengths 76A, 76B of the coatedoptical fibers 70A, 70B. As shown in FIG. 6, the solid overcoating 80may include tapered thickness ends 82A, 82B and a central section 86having a substantially constant outer diameter that exceeds an outerdiameter of the pre-coated optical fibers 70A, 70B, with the pre-coatedoptical fibers 70A, 70B including an outer diameter that includes thatof the previously stripped sections 74A, 74B embodying glass claddingmaterial.

As shown in FIG. 6, at least portions of the solid overcoating 80 ofpolymeric material include an outer diameter that exceeds an outerdiameter of the pre-coated optical fibers 70A, 70B. The coated opticalfibers 70A, 70B may each have a nominal outer diameter of 0.25 mm (250μm) in some embodiments. In certain embodiments, the solid overcoating80 of polymeric material may include an outer diameter in a range offrom 0.2 mm to 0.9 mm, or from 0.2 mm to 0.7 mm, or from 0.2 to 0.5 mm,or from 0.25 mm to 0.9 mm, or from 0.25 to 0.7 mm, or from 0.25 to 0.5mm.

Although only a single fusion spliced optical fiber 88 is shown in FIG.6, it is to be appreciated that a solid overcoating similar to thatshown in FIG. 6 may be applied to multiple fusion spliced optical fibersarranged in a one-dimensional array. In such a situation, theabove-described outer diameter values for solid overcoating of polymericmaterial may correspond to thickness values for the solid overcoatingapplied to an array of fusion spliced optical fibers.

In certain embodiments, the polymeric material comprises a thermoplasticmaterial that may be heated to a flowable state. In certain embodiments,the polymeric material in a flowable state comprises aphotopolymerizable adhesive, such as a UV-curable polymeric materialthat may be solidified by impingement of ultraviolet emissions thereon.In certain embodiments, a polymeric material may be devoid of UV-curablecomponents. In certain embodiments, the polymeric material in a flowablestate comprises a moisture-curable polymeric material or a two-partadhesive that may be solidified by supplying moisture or a curing agentto the polymeric material. In certain embodiments, fusion splicedoptical fibers may be temporarily placed in a cavity (e.g., a moldcavity), a housing, a trough, or a container in which polymeric materialin a flowable state is present, or to which polymeric material in aflowable state is supplied. In certain embodiments, fusion splicedoptical fibers may be dipped into a pool of molten thermoplasticmaterial as part of the contacting step. In certain embodiments, apolymeric material that may be used to overcoat portions of fusionspliced optical fibers may include one or more of polyamide, polyolefin,a polyamide-polyolefin copolymer, a polyamide grafted polyolefin, and acopolyester. Other polymeric materials (including thermoplasticmaterials) may be used. In certain embodiments, a polymeric materialthat may be used to overcoat portions of fusion spliced optical fibersmay include a melt-flow thermoplastic adhesive material.

In certain embodiments, a polymeric overcoating extending as disclosedherein is arranged over a splice joint, as well as over strippedsections and pre-coated sections of fusion spliced optical fibers (e.g.,including at least a short distance of acrylate coated sectionsproximate to the stripped sections). At least a portion of the polymericovercoating includes a diameter that exceeds a diameter of one or morepre-coated sections of the fusion spliced optical fibers. Exemplaryoptical fibers include 250 μm or 200 μm diameter acrylate coated fiberswithout any additional buffer layer.

A desirable polymeric overcoating material is preferably not subject todelamination during normal handling over the required service conditionsand lifetime of a fiber optic cable. In certain embodiments, flowablepolymeric material used to fabricate a polymeric overcoating comprisesmolten thermoplastic material. To avoid thermal degradation of one ormore acrylate coating layers of the pre-coated sections of the fusionspliced optical fibers, molten thermoplastic material to be used forovercoating should be maintained at a processing temperature below amelt temperature of the one or more acrylate coating layers. To promoteformation of a suitable overcoating, the molten thermoplastic materialmay also be maintained at a processing temperature at which the moltenthermoplastic material has a melt viscosity in a range of from about 100centipoises (cps) to about 10,000 cps, or more preferably in a subrangeof from about 1000 cps to about 10,000 cps, or more preferably in asubrange of from about 2000 cps to about 4000 cps.

In certain embodiments, desirable thermoplastic overcoating materialsdiffer from conventional melt flow adhesive glue sticks or typicalthermoplastic materials in that they should desirably: have a mediumviscosity (e.g., according to one or more of the ranges outlined above)at a processing temperature, be chemically stable at the processingtemperature, have a glass transition temperature of no greater than −40°C., have a service temperature spanning at least a range of from −40° C.to 85° C. without suffering significant mechanical and/or opticalperformance degradation, exhibit strong adhesion to fiber coating layersand bare glass, be free from charring, and/or exhibit minimal to nooutgassing (e.g., of volatile organic compounds and/or otherconstituents). A glass transition temperature is the point at which amaterial goes from a hard brittle state to a flexible or soft rubberystate as temperature is increased. A common method for determining glasstransition temperature uses the energy release on heating indifferential scanning calorimetry. If a plastic (e.g., thermoplastic)material associated with an optical fiber is exposed to a temperaturebelow its glass transition temperature, then the material will becomevery hard, and the optical fiber may be susceptible to micro bendlosses. In certain embodiments, service temperature of a thermoplasticovercoating material may be determined by compliance with one or moreindustry standards for telecommunication fiber reliability testing, suchas (but not limited to): ITU-T G.652, IED60793-2, Telcordia GR-20-COREand TIA/EIA-492.

Formation of a solid thermoplastic overcoating over at least a shortdistance of pre-coated sections of optical fibers bounding a splicedsegment (e.g., at either end of stripped sections joined at a splicejoint) beneficially ensures that all previously stripped (glass)sections are fully overcoated. In certain embodiments, a solidthermoplastic overcoating extends over a length of a pre-coated sectionof each of the first and second optical fibers, wherein the overcoatedlength of each pre-coated section is in a range of from about 1 mm toabout 10 mm. Additionally, since the solid thermoplastic overcoating mayadhere to one or more coating layers of an optical fiber more readilythan to (pre-stripped) exposed glass sections, providing a solidthermoplastic overcoating of sufficient length to overlap at least ashort distance of pre-coated sections of optical fibers bounding aspliced segment promotes more secure adhesion between the solidthermoplastic overcoating and the fusion spliced segment as a whole. Incertain embodiments, a solid thermoplastic overcoating and a fusionspliced segment utilize a thermoplastic material that is devoid ofadditives configured to promote adhesion to glass, such as silane. Asolid thermoplastic overcoating as disclosed herein is preferably notsubject to delamination during normal handling over the required serviceconditions and lifetime of a fiber optic cable.

In preferred embodiments, a solid thermoplastic overcoating iswater-resistant and serves to block moisture from reaching the splicejoint and the previously stripped glass region of a fusion splicedsegment of optical fibers. This is beneficial since moisture is known tochemically interact with glass cladding of optical fibers and causeexpansion of micro defects in the glass, thereby leading to long-termfailure of optical fibers. The solid thermoplastic overcoating ispreferably also devoid of sharp particles (e.g., inorganic fillerparticles) and air bubbles. The solid thermoplastic overcoating may alsobe devoid of a UV curable material. In certain embodiments, formation ofair bubbles may be reduced by contacting stripped sections andpre-coated sections of fusion spliced first and second optical fiberswith molten thermoplastic material in a subatmospheric pressureenvironment (e.g., in a range of from 0.01 to 0.9, or 0.1 to 0.8, or 0.1to 0.7 times local atmospheric pressure), such as may be attained in apartially evacuated chamber or other enclosure.

After a one-dimensional array of fusion spliced optical fibers is formed(and either before or after at least a portion of the stripped sectionsof the fusion spliced optical fibers are contacted with polymericmaterial in a flowable state), a position of a second group of fusionspliced optical fibers is altered relative to a positon of a first groupof fusion spliced optical fibers to yield a non-coplanar arrangement atthe fusion splice region. For example, an initial collection of twelvefusion spliced optical fibers may be used to form a two-dimensionalarray (e.g., a 3×4 array, a 2×6 array, or a hexagonal close-packedconfiguration) by altering position of a second group of fusion splicedoptical fibers (or second and third groups of fusion spliced opticalfibers) relative to a first group of fusion spliced optical fibers. Thealtering of position of at least some spliced optical fibers preferablyyields a non-coplanar arrangement. At the fusion splice region, a firstplane is definable through parallel fiber cores of a first group offusion spliced optical fibers of the plurality of fusion spliced opticalfibers, a second plane is definable through parallel fiber cores of asecond group of fusion spliced optical fibers of the plurality of fusionspliced optical fibers, and the first and second planes arenon-coplanar.

Because conventional encapsulated optical fiber ribbons are not amenableto being bent or folded, fiber optic cable assemblies and fabricationmethods disclosed herein preferably utilize loose optical fibers (e.g.,stranded optical fibers emanating from a cable jacket), a rollable orpliable fiber ribbon, or a standard fiber ribbon from which aninter-fiber polymer binding matrix has been (at least locally) removed.Thus, in certain embodiments, at a region distal from a fusion spliceregion, each group of optical spliced optical fibers may be embodied in(i) a rollable ribbon contained within a cable jacket or an encapsulant,(ii) a plurality of stranded optical fibers contained within a cablejacket, or (iii) a fiber ribbon from which an inter-fiber polymerbinding matrix has been (at least locally) removed.

In certain embodiments involving loose optical fibers (e.g., as mayemanate from a cable jacket containing stranded optical fibers), theloose fibers may be bonded by flexible polymer adhesives before beingprocessed by coating, stripping, cleaving, and mass fusion splicing.Such bonding provides dimensional stability to the loose fibers duringsubsequent steps of polymeric material overcoating/encapsulation as wellas positioning of optical fiber groups into a configuration other than aone-dimensional array. In such an embodiment, at least portions offlexible polymer adhesive material may be overcoated with polymericmaterial during one or more steps of polymeric material overcoating orencapsulation. In one embodiment involving a first group of loose,pre-coated (i.e., acrylate coated) optical fibers, the first group ofoptical fibers may be flexibly adhered into a first one-dimensionalflexible fiber array having a length of at least about 60 mm.Thereafter, coating material may be stripped from ends of the firstgroup of pre-coated optical fibers, and stripped ends of the first groupof pre-coated optical fibers may be cleaved to form stripped sections ofoptical fibers suitable for fusion splicing. If the first group ofoptical fibers is to be fusion spliced to a second group of loose,pre-coated optical fibers, then the second group of optical fibers maybe flexibly adhered into a second one-dimensional flexible fiber arrayhaving a length of at least about 60 mm. Thereafter, coating materialmay be stripped from ends of the second group of pre-coated opticalfibers, and stripped ends of the second group of pre-coated opticalfibers may be cleaved to form stripped sections of optical fibers alsosuitable for fusion splicing.

Various dimensions for stripped sections of optical fibers may beprovided. In certain embodiments, the stripped segment of each opticalfiber prior to fusion bonding has a length in a range of from 3 mm to 12mm, or from 5 mm to 11 mm, or 6 mm to 12 mm, or 8 mm to 11 mm. Followingfusion bonding between stripped segments, the stripped length portion ofeach fusion bonded optical fiber may be double the previously recitedranges (or about 20 mm in certain embodiments).

In certain embodiments, first and second pluralities of optical fiberssubject to being fusion spliced to one another. In certain embodiments,optical fibers of the first plurality of optical fibers have the samecoating diameter as optical fibers of the second plurality of opticalfibers. In certain embodiments, optical fibers of the first plurality ofoptical fibers have a first coating diameter that differs from a secondcoating diameter of optical fibers of the second plurality of opticalfibers. In certain embodiments, the first plurality of optical fibers isat least initially contained in a fiber optic cable of one type, and thefirst plurality of optical fibers is at least initially contained in afiber optic cable of the same type. In certain embodiments, the firstplurality of optical fibers is at least initially contained in a fiberoptic cable of a first type, and the first plurality of optical fibersis at least initially contained in a fiber optic cable of a second typethat differs from the first type.

As noted previously, the fabrication steps of (a) positioning one ormore groups of optical fibers into a configuration other than aone-dimensional array and (b) contacting at least a portion of thestripped sections of the fusion spliced optical fibers with polymericmaterial in a flowable state, may be performed in any suitable order. Incertain embodiments, the foregoing repositioning step (a) may beperformed prior to the contacting step (b). In certain embodiments, theforegoing contacting step (b) may be performed prior to therepositioning step (a). Following the preceding steps, the polymericmaterial is solidified. In certain embodiments, solidification of thepolymeric material serves to encapsulate all stripped sections of theplurality of fusion spliced optical fibers, as well as the fusion spliceregion and portions of the pre-coated sections of optical fibersproximate to the stripped sections.

In certain embodiments, the contacting at least a portion of thestripped sections of the fusion spliced optical fibers with polymericmaterial in a flowable state may include coating at least a portion ofthe stripped sections with a first portion of polymeric material priorto the altering of position of at least some spliced optical fibers ofthe plurality of fusion spliced optical fibers, and coating at least aportion of the stripped sections with a second portion of polymericmaterial in a flowable state after the altering of position of at leastsome spliced optical fibers of the plurality of fusion spliced opticalfibers. Restated, such a method may include an initial polymericmaterial contacting step, followed by positioning of groups of fusionspliced optical fibers into a configuration other than a one-dimensionalarray, followed by a subsequent polymeric material contacting step.

In certain embodiments, one or more after contacting at least a portionof the stripped sections of the fusion spliced optical fibers withpolymeric material in a flowable state, the polymeric material may be atleast partially solidified, followed by reflowing at least a portion thepolymeric material (e.g., by reheating of a thermoplastic material)(with the reflowing optionally including incorporation of additionalpolymeric material), and followed by full solidification of the reflowedpolymeric material. Such reflowing may be beneficial in cases where apolymeric material is partially hardened around a one-dimensional arrayof fusion spliced optical fibers, and groups of fusion spliced opticalfibers overcoated with partially hardened thermoplastic material arestacked onto or otherwise contacted with one another.

Various methods may be used to alter position of at least some fusionspliced optical fibers. In certain embodiments, mass fusion splicedfibers may be overcoated with thermoplastic material and separated intoa number of subarrays each including multiple coated optical fibers. Thesubarrays are then stacked in a fixture, and polymer coated spliceregions are heated above the melt flow temperature of the thermoplasticmaterial and subsequently cooled. Such process causes the thermoplasticovercoating between the subarrays to coalesce and form an encapsulatedtwo-dimensional high density encapsulated splice.

In certain embodiments, the altering of position of at least somespliced optical fibers of a plurality of fusion spliced optical fibersincludes rolling the at least some spliced optical fibers in a directionperpendicular to fiber cores of the spliced optical fibers. Such a stepmay be useful for forming an overcoated fiber optic cable portion havinga cross-section in a hexagonal close-packed configuration. In certainembodiments, such rolling may be combined with twisting to form anovercoated fiber optic cable portion having optical fibers arranged in aspiral configuration.

In certain embodiments, the altering of position of at least somespliced optical fibers of a plurality of fusion spliced optical fibersincludes a folding a first group fusion spliced optical fibers (e.g., ina direction perpendicular to fiber cores of fusion spliced opticalfibers) in a manner causing the first group of fusion spliced opticalfibers to overlie the second group of fusion spliced optical fibers.Such a step may be useful for forming an overcoated fiber optic cableportion having a cross-section with a rectangular shape. As analternative to folding, in certain embodiments the altering of positionof at least some spliced optical fibers of a plurality of fusion splicedoptical fibers may include stacking a first group of fusion splicedoptical fibers over a second group of fusion spliced optical fibers.

FIGS. 7A and 7B illustrate a heating apparatus 102 useable for coatingmultiple fusion spliced optical fibers 120 with thermoplastic material.The multiple fusion spliced optical fibers 120 are composed of a firstgroup of optical fiber segments 120A and a second group of optical fibersegments 120B, with ends of stripped sections 124A, 124B of the opticalfiber segments 120A, 120B being fusion spliced at a fusion splice region122. The heating apparatus 102 includes a body 104 that contains aninternal electric cartridge heater 105. A pool of molten thermoplasticmaterial 90 is arranged atop a substantially level, flat heated surface106. Lateral edges 91A, 91B of the pool of molten thermoplastic material90 extend to lateral edges 108A, 108B of the flat heated surface 106without overflowing, due to lower temperature at the lateral edges 108A,108B as well as surface tension of the molten thermoplastic material 90.FIG. 7A illustrates the fusion spliced optical fibers 120 arranged abovethe pool of molten thermoplastic material 90, with the splice joint 122roughly centered above the pool, and with the length of the poolexceeding the combined length of the stripped sections 124A, 124B. Asshown, a first side 126A of the fused optical fibers 120 initiallycontacts the pool of molten thermoplastic material 90, while the secondside 126B of the fusion spliced optical fibers 120 remains elevatedabove the pool. Thereafter, the remainder of the fusion spliced opticalfibers 120 gradually tilts to a more horizontal orientation and issubmerged into the pool, as shown in FIG. 7B. Such figure shows thestripped sections 124A, 124B and the splice joint 122 of the fusionspliced optical fibers 120 submerged in the pool of molten thermoplasticmaterial 90.

Thereafter, the multiple fusion spliced optical fibers 120 may beremoved from the pool of molten thermoplastic material 90 insubstantially a reverse manner from which it was introduced into thepool, and the molten liquid contacting the fusion spliced optical fibers120 may be cooled to yield a solid thermoplastic overcoating thatextends over the previously stripped sections 124A, 124B, the spliceregion 122, and portions of the first and second pluralities of opticalfiber segments 120A, 120B that were previously unstripped. In certainembodiments, the solid thermoplastic overcoating may comprise amelt-flow thermoplastic adhesive material, such as TECHNOMELT® PA 6208polyamide material (Henkel Corp., Dusseldorf, Germany). Such materialexhibits a heat resistance temperature greater than 90° C., a melt flowtemperature lower than 260° C., a melt viscosity between 100 cps and10,000 cps, and a hardness of at least Shore A 45. Further detailsregarding thermoplastic overcoating of fusion spliced optical fibersand/or portions of fiber optic cable assemblies are disclosed inInternational Application No. PCT/US2018/021685 filed on Mar. 9, 2018,wherein the content of the foregoing application is hereby incorporatedby reference herein.

FIGS. 8A and 8B provide perspective and cross-sectional views,respectively, of a fiber optic cable 130 with twelve fusion splicedoptical fibers 132 arranged in a 3×4 array, and overcoating material 134that extends over stripped sections 136A, 136B of the fusion splicedoptical fibers 132 and a fusion splice region 138. The fusion splicedoptical fibers 132 include first and second pluralities of fiber opticsegments 132A, 132B that each include a pre-coated section 140A, 140Band a stripped section 136A, 136B, with ends of the stripped sections136A, 136B being fusion spliced to one another at the fusion spliceregion 138. The overcoating material 134 has a length L sufficient tocover not only the stripped sections 136A, 136B and the fusion spliceregion 138, but also portions of the pre-coated sections 140A, 140B ofthe fusion spliced optical fibers 132 to form overlap regions 142A,142B. FIG. 8B provides a cross-sectional view taken through one of theseoverlap regions 142A. Referring to FIG. 8B, in the overlap region 142A,each fusion spliced optical fiber 132 includes a glass core 144, glasscladding 146, and an acrylate coating 148. As shown, the acrylatecoating 148 of each optical fiber 132 may be arranged in contact with anacrylate coating of at least one other optical fiber within the 3×4array; however, in the stripped sections 136A, 136B of FIG. 8A, thestripped (glass) sections 136A, 136B are arranged in parallel withoutcontacting one another, and the overcoating material 134 directlycontacts glass material (i.e., cladding material 146 as shown in FIG.8B) of the stripped sections 136A, 136B. With continued reference toFIG. 8B, the array of optical fibers 132 may be segregated in threeoptical fiber groups 145-1, 145-2, 145-3. Within each optical fibergroup 145-1, 145-2, 145-3, a plane P₁, P₂, P₃ is definable through glasscores 144 of at least two (or as illustrated, three) optical fibers ofthat group. As shown, the three planes P₁, P₂, P₃ are non-coplanar. The3×4 array configuration of fusion spliced optical fibers 132 shown inFIGS. 8A and 8B is significantly narrower than a width that would resultfrom arranging the twelve fusion spliced optical fibers 132 in a onedimensional (i.e., 1×12) array. In certain embodiments, the maximumcross-sectional dimension (e.g., maximum width) of an encapsulated areaof the fiber optic cable 130 (e.g., corresponding to one of the overlapregions 142A, 142B) is within a diameter of 1.3 mm, which enables thefiber optic cable 130 to easily fit into the 1.5 mm inner diameter of a2 mm outer diameter cable jacket. This dimension is significantlyreduced in comparison to the 3.1 mm width of a standard optical fiberribbon.

FIGS. 9A and 9B provide perspective and cross-sectional views,respectively, of a fiber optic cable 150 with twelve fusion splicedoptical fibers 152 arranged in a 2×6 array, and overcoating material 154that extends over stripped sections 156A, 156B of the fusion splicedoptical fibers 152 and over a fusion splice region 158. The fusionspliced optical fibers 152 include first and second pluralities of fiberoptic segments 152A, 152B that each include a pre-coated section 160A,160B and a stripped section 156A, 156B, with ends of the strippedsections 156A, 156B being fusion spliced to one another at the fusionsplice region 158. The overcoating material 154 has a length Lsufficient to cover not only the stripped sections 156A, 156B and thefusion splice region 158, but also portions of the pre-coated sections160A, 160B of the fusion spliced optical fibers 152 to form overlapregions 162A, 162B. FIG. 9B provides a cross-sectional view takenthrough one of these overlap regions 162A. Referring to FIG. 9B, in theoverlap region 162A, each fusion spliced optical fiber 152 includes aglass core, glass cladding 166, and an acrylate coating 168. As shown,the acrylate coating 168 of each optical fiber 152 may be arranged incontact with an acrylate coating of at least one other optical fiberwithin the 2×6 array; however, in the stripped sections 156A, 156B ofFIG. 9A, the stripped (glass) sections 156A, 156B are arranged inparallel without contacting one another, and the overcoating material154 directly contacts glass material (i.e., cladding material 166 asshown in FIG. 9B) of the stripped sections 156A, 156B. With continuedreference to FIG. 9B, the array of optical fibers 152 may be segregatedin two optical fiber groups 165-1, 165-2. Within each optical fibergroup 165-1, 165-2, a plane P₁, P₂, is definable through glass cores ofat least two (or as illustrated, six) optical fibers of that group. Asshown, the two planes P₁, P₂ are non-coplanar. The 2×6 arrayconfiguration of fusion spliced optical fibers 152 shown in FIGS. 9A and9B is significantly narrower than a width that would result fromarranging the twelve fusion spliced optical fibers 152 in a 1×12 array(although not as narrow as the 3×4 array configuration shown in FIGS. 8Aand 8B). The fusion spliced optical fibers 152 shown in FIGS. 9A and 9Bis amenable to being positioned in the depicted 2×6 array configurationby two-layer folding, which is relatively simple among variouspositioning methods disclosed herein. A tradeoff associated with thisease of manufacture is that the fiber optic cable 150 exhibits reducedstiffness against bending along the short axis, separately from thelarger width relative to the embodiment of FIGS. 8A-8B. In certainembodiments, the maximum cross-sectional dimension of an encapsulatedarea of the fiber optic cable 150 (e.g., corresponding to one of theoverlap regions 162A, 162B) is 1.67 mm, which enables the fiber opticcable 150 to easily fit into a 3 mm outer diameter cable jacket.

FIGS. 10A and 10B provide perspective and cross-sectional views,respectively, of a fiber optic cable 170 with twelve fusion splicedoptical fibers 172 arranged in a hexagonal close packed four-layerconfiguration, and overcoating material 174 that extends over strippedsections 176A, 176B of the fusion spliced optical fibers 172 and over afusion splice region 178. The fusion spliced optical fibers 172 includefirst and second pluralities of fiber optic segments 172A, 172B thateach include a pre-coated section 180A, 180B and a stripped section176A, 176B, with ends of the stripped sections 176A, 176B being fusionspliced to one another at the fusion splice region 178. The overcoatingmaterial 174 has a length L sufficient to cover not only the strippedsections 176A, 176B and the fusion splice region 178, but also portionsof the pre-coated sections 180A, 180B of the fusion spliced opticalfibers 172 to form overlap regions 182A, 182B. FIG. 10B provides across-sectional view taken through one of these overlap regions 182A.Referring to FIG. 10B, in the overlap region 182A, each fusion splicedoptical fiber 172 includes a glass core 184, glass cladding 186, and anacrylate coating 188. As shown, the acrylate coating 188 of each opticalfiber 172 may be arranged in contact with an acrylate coating of atleast one other optical fiber within the hexagonal close packedfour-layer configuration; however, in the stripped sections 176A, 176Bof FIG. 10A, the stripped (glass) sections 176A, 176B are arranged inparallel without contacting one another, and the overcoating material174 directly contacts glass material (i.e., cladding material 186 asshown in FIG. 10B) of the stripped sections 176A, 176B. With continuedreference to FIG. 10B, the hexagonal close packed four-layerconfiguration of optical fibers 172 may be segregated in four opticalfiber groups 185-1, 185-2, 185-3, 185-4. Within each optical fiber group185-1, 185-2, 185-3, 185-4, a plane P₁, P₂, P₃, P₄ is definable throughglass cores 184 of at least two (or as illustrated, three or four incertain instances) optical fibers of that group. As shown, the fourplanes P₁, P₂, P₃, P₄ are non-coplanar. The hexagonal close packedfour-layer configuration of fusion spliced optical fibers 172 shown inFIGS. 10A and 10B is significantly narrower than a width that wouldresult from arranging the twelve fusion spliced optical fibers 172 in a1×12 array, and also narrower than 3×4 and 2×6 array configurationsshown in FIGS. 8A-8B and FIGS. 9A-9B. In certain embodiments, themaximum cross-sectional dimension of an encapsulated area of the fiberoptic cable 170 (e.g., corresponding to one of the overlap regions 182A,182B) is 1.0 mm, which enables the fiber optic cable 150 to easily fitinto a 3 mm outer diameter cable jacket.

As noted previously herein, in certain embodiments loose fibers may bebonded by flexible polymer adhesives before being processed by coating,stripping, cleaving, and mass fusion splices, with such bonding beinguseful to provide dimensional stability of the fibers during subsequentprocessing steps. FIG. 11A is a perspective view of a portion of a fiberoptic cable subassembly 189 during fabrication, with twelve fusionspliced optical fibers 192 arranged in a one-dimensional array, andbeing devoid of overcoating material over stripped sections 196A, 196Bof the fusion spliced optical fibers 192. The fusion spliced opticalfibers 192 include first and second pluralities of fiber optic segments192A, 192B that each include a pre-coated section 200A, 200B and astripped section 196A, 196B, with ends of the stripped sections 196A,196B being fusion spliced to one another at the fusion splice region198. As shown, flexible polymer adhesive binding material regions 193A,193B are provided over portions of the pre-coated sections 200A, 200B ofthe first and second pluralities of fiber optic segments 192A, 192B. Incertain embodiments, flexible polymer adhesive binding material 193A,193B may be used to flexibly adhere fiber optic segments of the firstand second pluralities of fiber optic segments 192A, 192B prior tostripping of acrylate coating material from ends of the fiber opticsegments 192A, 192B, and prior to cleaving of stripped ends of fiberoptic segments 192A, 192B. At least portions of flexible polymeradhesive binding material regions 193A, 193B are subject to beingsubsequently overcoated with polymeric material during overcoating ofthe stripped segments 196A, 196B and the fusion splice region 198.

FIG. 11B illustrates a fiber optic cable 190 incorporating thesubassembly of FIG. 11A, following formation of a polymeric overcoating194 extending over the stripped segments 196A, 196B and the fusionsplice region 198. The polymeric overcoating 194 further extends overportions of the flexible polymer adhesive binding material regions 193A,193B to form polymeric material overlap regions 195A, 195B. In certainembodiments, a length of each polymeric material overlap region 195A,195B is at least about 3 mm in a direction parallel to fiber cores ofthe fusion spliced optical fibers 192. The remaining elements of FIG.11B are identical to those described in FIG. 11A, and will not bedescribed again for sake of brevity.

FIG. 12A is a perspective view of a portion of a fiber optic cablesubassembly 210 during fabrication, showing a two-dimensional array ofmultiple fusion spliced optical fibers in a process of being formed byrolling (by application of a rolling force F) in a directionperpendicular to cores of multiple fusion spliced optical fibers 212.The fusion spliced optical fibers 212 include first and secondpluralities of fiber optic segments 212A, 212B that each include apre-coated section 220A, 220B and a stripped section 216A, 216B, withends of the stripped sections 216A, 216B being fusion spliced to oneanother at the fusion splice region 218. Overcoating material 214extends over stripped sections 216A, 216B of the fusion spliced opticalfibers 212, over the fusion splice region 218, and over portions of thepre-coated sections 220A, 220B to form overlap regions 222A, 222B. Asshown, a second group of overcoated fusion spliced optical fibers 217Bis taller than a first group of overcoated fusion spliced optical fibers217A, such that with continued rolling of the second group of overcoatedfusion spliced optical fibers 217B by application of the rolling forceF, the second group of overcoated fusion spliced optical fibers 217B mayoverlap the first group of overcoated fusion spliced optical fibers217A. If the overcoating material 214 embodies thermoplastic material,then in certain embodiments, reheating of the overcoating material 214may cause reflow of the overcoating material 214 between the first andsecond groups of overcoated fusion spliced optical fibers 217A, 217Bsufficient to adhere these groups together after cooling of theovercoating material 214.

FIG. 12B is a perspective view of a portion of a fiber optic cablesubassembly 230 during fabrication, showing an overcoated second groupof fusion spliced optical fibers 237B in a state of being folded, withthe intention of subsequently being positioned to overlap an overcoatedfirst group of fusion spliced optical fibers 237A. The fusion splicedoptical fibers encompass first and second pluralities of fiber opticsegments 242A, 242B that each include a pre-coated section 240A, 240Band a stripped section 236A, 236B, with ends of the stripped sections236A, 236B being fusion spliced to one another at the fusion spliceregion 238. Overcoating material 234 extends over the stripped sections236A, 236B, over the fusion splice region 238, and over portions of thepre-coated sections 240A, 240B to form overlap regions 242A, 242B. Asshown, a second group of overcoated fusion spliced optical fibers 237Bis vertically oriented and extends higher than a first group ofhorizontally arranged overcoated fusion spliced optical fibers 237A.With continued folding of the second group of overcoated fusion splicedoptical fibers 237B by application of the folding force F, the secondgroup of overcoated fusion spliced optical fibers 237B may be stackedatop the first group of overcoated fusion spliced optical fibers 237A.If the overcoating material 234 embodies thermoplastic material, then incertain embodiments, reheating of the overcoating material 234 may causereflow of the overcoating material 234 between the first and secondgroups of overcoated fusion spliced optical fibers 237A, 237B sufficientto adhere these groups together after cooling of the overcoatingmaterial 234.

FIG. 13 is a perspective view of a portion of an overcoated fiber opticcable 260 arranged on a heated surface 256 during a fabrication step, tocause reflow of thermoplastic overcoating material 274. A group oftwelve fusion spliced optical fibers 252 are arranged in atwo-dimensional array, and include first and second pluralities of fiberoptic segments 252A, 252B that each include a pre-coated section 260A,260B and a stripped section 256A, 256B. Ends of the stripped sections256A, 256B are fusion spliced to one another at the fusion splice region258. Thermoplastic overcoating material 254 extends over strippedsections 216A, 216B of the fusion spliced optical fibers 252, over thefusion splice region 258, and over portions of the pre-coated sections270A, 270B to form overlap regions 272A, 272B. As shown, a centralportion of the cable 260 is arranged on an upper surface 256 of aheating apparatus 252 (which may include a metal body with an internalelectric cartridge heater). Contact between the overcoating material 254and the upper surface 256 of the heating apparatus 252 will enable theovercoating material 254 to reflow when it reaches the melt flowtemperature of the overcoating material 254. Such reflow may promotedistribution of overcoating material 254 and adhesion between differentgroups of the fusion spliced optical fibers 252. Proximal overlapsubregions 273A, 273A may also experience reflow due to contact with theupper surface 256 of the heating apparatus 252. Upon cooling of theovercoating material 254 applied to the fiber optic cable 260, theovercoating material 254 will harden to a solid state sufficient toprotect the fusion splice region 268 and the stripped sections 256A,256B.

EXAMPLE

With reference to FIG. 14A, sets of twelve optical fibers 292A, 292Bemanating from two loose tube cables are fusion spliced together at afusion splice region 294. The fusion splice region 294 and strippedsections of the optical fibers 292A, 292B are overcoated (encapsulated)with polymeric material 295 and arranged in a hexagonal close packedfour-layer configuration to form a fiber optic cable 290. Color patternson both sides of the fusion splice region 294 match very well,suggesting that optical fibers 292A, 292B at the fusion splice region294 are parallel without crossing. The fiber optic cable 290 is comparedto a ribbon spliced cable 280 including first and second optical fiberribbons 282A, 282B spliced in a one-dimensional array format at a fusionsplice region 284 and protected with a conventional heat shrink spliceprotector 284. FIG. 14A shows that the novel fiber optic cable 290exhibits a dramatic reduction in width/diameter and a concomitantimprovement in density.

FIG. 14B illustrates the fiber optic cable 290 of FIG. 14A bent into atight radius to demonstrate that the overcoating 295 and fusion spliceregion 294 exhibit greater stiffness than non-overcoated loose fibers292A, 292B. FIG. 14B thus illustrates the stiffness resulting from theself-reinforcement effect of the packed array multi-fiber splice.Without using any external strength member, the multi-fiber fusionsplice region 294 of FIG. 14B maintains straightness when the rest ofthe optical fibers 292A, 292B are bent to a diameter of less than 50 mm.

Those skilled in the art will appreciate that various modifications andvariations can be made without departing from the spirit or scope of theinvention. Since modifications, combinations, sub-combinations, andvariations of the disclosed embodiments incorporating the spirit andsubstance of the invention may occur to persons skilled in the art, theinvention should be construed to include everything within the scope ofthe appended claims and their equivalents. The claims as set forth beloware incorporated into and constitute part of this detailed description.

It will also be apparent to those skilled in the art that unlessotherwise expressly stated, it is in no way intended that any method inthis disclosure be construed as requiring that its steps be performed ina specific order. Accordingly, where a method claim below does notactually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is no way intended thatany particular order be inferred.

What is claimed is:
 1. A fiber optic cable, comprising: a plurality offusion spliced optical fibers, wherein each fusion spliced optical fiberof the plurality of fusion spliced optical fibers includes two opticalfiber segments joined together by a fusion splice, and each opticalfiber segment includes a stripped section proximate to the fusion splicejoining the two optical fiber segments; and a polymeric overcoatingcontacting, surrounding, and extending over the fusion splices of theplurality of fusion spliced optical fibers and over the stripped sectionof each optical fiber segment; wherein the fusion splices of theplurality of fusion spliced optical fibers define a fusion splice regionof the fiber optic cable, and the plurality of fusion spliced opticalfibers has a non-coplanar arrangement at the fusion splice region; thepolymeric overcoating is substantially continuous and encapsulates thestripped section of each optical fiber segment of the plurality offusion spliced optical fibers; and the polymeric overcoating comprises amaximum width of no greater than 2 mm in a widthwise direction that isperpendicular to a lengthwise direction of the fiber optic cable.
 2. Thefiber optic cable of claim 1, wherein the plurality of fusion splicedoptical fibers comprises at least four fusion spliced optical fibers. 3.The fiber optic cable of claim 1, wherein the polymeric overcoatingcomprises a length of no greater than about 30 mm in a lengthwisedirection of the fiber optic cable.
 4. The fiber optic cable of claim 1,wherein each optical fiber segment of the plurality of fusion splicedoptical fibers includes a pre-coated section, and the polymericovercoating further extends over a portion of the pre-coated section ofeach optical fiber segment.
 5. The fiber optic cable of claim 1, whereinat a region distal from the fusion splice region, each group of fusionspliced optical fibers is embodied in (i) a rollable or pliable opticalfiber ribbon contained within a cable jacket or an encapsulant, or (ii)a plurality of stranded optical fibers contained within a cable jacketor an encapsulant.
 6. The fiber optic cable of claim 1, wherein thepolymeric overcoating comprises a thermoplastic polymer.
 7. The fiberoptic cable of claim 6, wherein the thermoplastic polymer has a heatresistance temperature greater than 90° C., a melt flow temperaturelower than 260° C., a melt viscosity between 100 cps and 10,000 cps, anda hardness of at least Shore A
 45. 8. The fiber optic cable of claim 1,wherein the polymeric overcoating comprises a UV curable adhesive, amoisture curable adhesive, or a two-part adhesive.
 9. The fiber opticcable of claim 1, being devoid of at least one of the following: (i)heat shrink tubing arranged over the fusion splice region, or (ii) astrength member extending over the fusion splice region.
 10. A fiberoptic cable, comprising: first and second groups of fusion splicedoptical fibers, wherein each fusion spliced optical fiber includes twooptical fiber segments joined together by a fusion splice, each opticalfiber segment includes a stripped section proximate to the fusion spliceof a corresponding fusion spliced optical fiber; and a polymericovercoating contacting, surrounding, and extending over the fusionsplices and over the stripped section of each optical fiber segment;wherein: the fusion splices define a fusion splice region of the fiberoptic cable; the first group and the second group of fusion splicedoptical fibers are arranged in respective first and second planes at thefusion splice region, the first and second planes extend in a lengthwisedirection of the fiber optic cable and are definable through fiber coresof the respective first group and second group of fusion spliced opticalfibers; and the first and second planes are non-coplanar; each opticalfiber segment includes a pre-coated section, and the polymericovercoating further extends over a portion of the pre-coated section ofeach optical fiber segment, the polymeric overcoating further extends alength of at least 3 mm over the pre-coated section of each opticalfiber segment.
 11. The fiber optic cable of claim 10, further comprisinga third group of fusion spliced optical fibers, wherein: the third groupof fusion spliced optical fibers is arranged in a third plane at thefusion splice region; the third plane is definable through fiber coresof the third group of fusion spliced optical fibers; and the first,second, and third planes are non-coplanar.
 12. The fiber optic cable ofclaim 10, wherein each of the first group and the second group of fusionspliced optical fibers comprises at least three fusion spliced opticalfibers.
 13. The fiber optic cable of claim 10, wherein: the polymericovercoating is substantially continuous and encapsulates the strippedsection of each optical fiber segment of the first and second groups offusion spliced optical fibers; and the polymeric overcoating comprises amaximum width of no greater than 2 mm in a widthwise direction that isperpendicular to a lengthwise direction.
 14. The fiber optic cable ofclaim 10, wherein the polymeric overcoating comprises a length of nogreater than about 30 mm in a lengthwise direction of the fiber opticcable.
 15. The fiber optic cable of claim 10, wherein: the strippedsection of each optical fiber segment has a length in a range of from 3mm to 12 mm.
 16. The fiber optic cable of claim 10, wherein at a regiondistal from the fusion splice region, each group of fusion splicedoptical fibers is embodied in a rollable or pliable optical fiber ribboncontained within a cable jacket or an encapsulant.
 17. The fiber opticcable of claim 10, wherein at a region distal from the fusion spliceregion, each group of fusion spliced optical fibers is embodied in aplurality of stranded optical fibers contained within a cable jacket.18. The fiber optic cable of claim 10, wherein the polymeric overcoatingcomprises a thermoplastic polymer.
 19. The fiber optic cable of claim18, wherein the thermoplastic polymer has a heat resistance temperaturegreater than 90° C., a melt flow temperature lower than 260° C., a meltviscosity between 100 cps and 10,000 cps, and a hardness of at leastShore A
 45. 20. The fiber optic cable of claim 11, wherein the polymericovercoating comprises a UV curable adhesive, a moisture curableadhesive, or a two part adhesive.
 21. The fiber optic cable of claim 11,being devoid of heat shrink tubing arranged over the fusion spliceregion.
 22. The fiber optic cable of claim 11, being devoid of astrength member extending over the fusion splice region.
 23. The fiberoptic cable of claim 1, wherein the plurality of fusion spliced opticalfibers are in contact with each other.